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Gene therapy SK195_5 Human genetics and health issues Gene therapy Page 2 of 31 2nd March 2016 http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-therapy/contentsection-0 Gene therapy About this free course This free course provides a sample of Level 1 study in Science: http://www.open.ac.uk/courses/find/science. This version of the content may include video, images and interactive content that may not be optimised for your device. You can experience this free course as it was originally designed on OpenLearn, the home of free learning from The Open University - www.open.edu/openlearn/sciencemaths-technology/science/biology/gene-therapy/content-section-0. There you’ll also be able to track your progress via your activity record, which you can use to demonstrate your learning. The Open University, Walton Hall, Milton Keynes, MK7 6AA Copyright © 2016 The Open University Intellectual property Unless otherwise stated, this resource is released under the terms of the Creative Commons Licence v4.0 http://creativecommons.org/licenses/by-ncsa/4.0/deed.en_GB. Within that The Open University interprets this licence in the following way: www.open.edu/openlearn/about-openlearn/frequently-askedquestions-on-openlearn. Copyright and rights falling outside the terms of the Creative Commons Licence are retained or controlled by The Open University. Please read the full text before using any of the content. We believe the primary barrier to accessing high-quality educational experiences is cost, which is why we aim to publish as much free content as possible under an open licence. If it proves difficult to release content under our preferred Creative Commons licence (e.g. because we can’t afford or gain the clearances or find suitable alternatives), we will still release the materials for free under a personal end-user licence. This is because the learning experience will always be the same high quality offering and that should always be seen as positive – even if at times the licensing is different to Creative Commons. When using the content you must attribute us (The Open University) (the OU) and any identified author in accordance with the terms of the Creative Commons Licence. The Acknowledgements section is used to list, amongst other things, third party (Proprietary), licensed content which is not subject to Creative Commons licensing. Proprietary content must be used (retained) intact and in context to the content at all times. Page 3 of 31 2nd March 2016 http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-therapy/contentsection-0 Gene therapy The Acknowledgements section is also used to bring to your attention any other Special Restrictions which may apply to the content. For example there may be times when the Creative Commons Non-Commercial Sharealike licence does not apply to any of the content even if owned by us (The Open University). In these instances, unless stated otherwise, the content may be used for personal and non-commercial use. We have also identified as Proprietary other material included in the content which is not subject to Creative Commons Licence. These are OU logos, trading names and may extend to certain photographic and video images and sound recordings and any other material as may be brought to your attention. Unauthorised use of any of the content may constitute a breach of the terms and conditions and/or intellectual property laws. We reserve the right to alter, amend or bring to an end any terms and conditions provided here without notice. All rights falling outside the terms of the Creative Commons licence are retained or controlled by The Open University. Head of Intellectual Property, The Open University The Open University Printed and bound in the United Kingdom at the University Press, Cambridge. 978-1-4730-0988-2 (.epub) 978-1-4730-1756-6 (.kdl) Page 4 of 31 2nd March 2016 http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-therapy/contentsection-0 Gene therapy Contents Introduction Learning outcomes 1 Genetic medicine: dreams and realities 2 Gene therapy 3 Somatic gene therapy 4 Germline gene therapy 5 Designer babies? Conclusion Keep on learning Acknowledgements Page 5 of 31 2nd March 2016 http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-therapy/contentsection-0 Gene therapy Introduction Following on from the advances made in diagnosing disorders using genetic testing, this course looks at the possibilities for genetic therapies. Two approaches to gene therapy are discussed: correcting genes involved in causing illness; and using genes to treat disorders. Before closing on a discussion of the issues around 'designer babies' somatic gene therapy and germline gene therapy are discussed. This OpenLearn course provides a sample of Level 1 study in Science. Page 6 of 31 2nd March 2016 http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-therapy/contentsection-0 Gene therapy Learning outcomes After studying this course, you should be able to: understand some of the types of disease that might be treatable by gene therapy understand the basic principals of genetic manipulation understand the differences between somatic and germline gene therapy and some of the problems involved in these potential treatments understand how genetics may be used in the design of drugs. Page 7 of 31 2nd March 2016 http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-therapy/contentsection-0 Gene therapy 1 Genetic medicine: dreams and realities Genetics can be used in medicine to confirm a previous or make a fresh diagnosis, or predict a disorder likely to occur in future. At the moment, that is often all that can be done. The so-called ‘diagnostic therapeutic gap’ is one immediate problem for us to deal with. When the only options on offer after a genetic test are to terminate a pregnancy, or prepare to deal with the disease as best you can, some of the dilemmas of new genetic knowledge are sharper. Genetic testing is only the beginning of the effect of genetics on medicine. What about treatment? This course looks at various ways in which the new knowledge of the human genome will affect how illnesses are treated. These treatments are already getting underway. We look at the one that gets talked about most — gene therapy — but also at other possibilities, which may be more important in the short term. These include using information about a person's genotype to prescribe drugs more closely tailored to their body chemistry. Before you move on to the next page, watch the following video clip that describes the process of fertilization. Video content is not available in this format. Page 8 of 31 2nd March 2016 http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-therapy/contentsection-0 Gene therapy 2 Gene therapy Gene therapy is often reported to be one of the most hopeful lines of experimentation to grow up alongside the Human Genome Project. If we know so much about all these genes, surely we can use this knowledge to try to treat some diseases in which genes are involved at a fundamental level? But what exactly is gene therapy, and where is the work heading? Just looking at the two words coupled in the phrase ‘gene therapy’ raises an important ambiguity. SAQ 1 From what you have learnt so far, what might gene therapy mean? View answer - SAQ 1 It turns out that it means both. Most of the public debate has been about the former meaning, i.e. correcting or repairing genes, but early applications have focused on the latter meaning. These applications involve using ‘designer’ DNA to tackle diseases that are not inherited – by using altered viruses designed specifically to attack cancer cells, say. Here, the DNA is working more or less like a drug. In fact, many ‘gene therapy’ trials approved so far have been attempts to treat a variety of cancers. Here, though, we will focus on the first of the two meanings of gene therapy, correcting genes. Some genetic diseases can be tackled by modifying the phenotype, without worrying about how DNA might be involved. Most simply, a multifactorial problem like a cleft palate can be corrected surgically. But for many diseases, such as cystic fibrosis (CF), non-genetic treatments can help to alleviate some symptoms, but so far that is all. So in a single-gene disorder such as CF, the theoretical focus is now on the gene and its product. We begin by focusing on gene products, i.e. proteins, and then consider genes. If the product, that is a particular protein, is abnormal, can it be corrected? If it is missing altogether, can it be supplied? Sometimes, the answer involves genetic manipulation (or genetic modification) of other organisms. This technique is described in Study Note 1. Study Note 1: The technique of genetic manipulation of organisms The technique of genetic manipulation, or genetic modification, of organisms relies on restriction enzymes to cut large molecules of DNA in order to isolate the gene or genes of interest from human DNA, which has been extracted from cells. After the gene has been isolated, it is inserted into bacterial cells and cloned. This process enables large amounts of identical copies of the human DNA to be extracted for further experiments. Once inside the bacterial cells, if the human gene is active or Page 9 of 31 2nd March 2016 http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-therapy/contentsection-0 Gene therapy ‘switched on’ then the bacteria behave like ‘living factories’, manufacturing large amounts of the human protein encoded by the gene (Figure 1). This can be extracted and purified from the bacterial cultures, ready for use by humans. Genetic manipulation has enabled unlimited quantities of certain human proteins to be produced more easily and less expensively than was previously possible. Problems exist with this approach, however, as proteins must fold themselves up into very specific structures to have a biological effect. Often this doesn't happen very effectively in bacteria. In order to overcome this problem, the cloned human DNA has been introduced into sheep. In this case, the human protein is secreted into the milk, allowing for a continuous process of production (Figure 1). Alternatively, the cloned human DNA can be used for gene therapy by direct intervention in the individual's DNA (Figure 1 and Study Note 2. Figure 1 The technique of genetic manipulation or genetic modification of organisms View description - Figure 1 The technique of genetic manipulation or genetic modification of ... Page 10 of 31 2nd March 2016 http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-therapy/contentsection-0 Gene therapy Human clotting factor, the protein used to treat haemophilia, can be made by splicing the human gene into bacteria (Figure 1). Insulin, which is used to treat diabetes, can be produced by sheep in their milk. Then you can supply the missing gene product to the patient like any other medicine. The methods of using either bacteria or sheep, like others involving production of genetically modified organisms for food, have been controversial in their way. Much of the technology involved in making genetically manipulated or modified organisms, involves doing the same sort of thing – inserting DNA into cells – as involved in gene therapy (as shown in Figure 1). SAQ 2 However, this technology is not gene therapy proper. Why not? View answer - SAQ 2 Suppose you could inject the gene instead – to provide direct intervention in the individual's DNA. SAQ 3 Even if you could get a new gene into a human, what else would be needed to make sure it worked as a therapy? View answer - SAQ 3 There is no point making haemoglobin in skin cells, or in producing in blood cells the protein that CF patients need in the lining of their lungs. And ideally it would have to go on working, perhaps in the cells’ descendants, otherwise repeat treatments would be needed. The idea of, in effect, treating the genotype, has been around from the 1960s. Since the new technologies of genetic manipulation came into widespread use in the 1980s, many trials of gene therapy have been carried out on humans. Despite high hopes, few have yet shown clear benefits to patients. At the turn of the millennium, it looked as though gene therapy would be more complicated, and take longer to deliver, than was thought 10 or 20 years previously. On the other hand, it may turn out that the techniques now being tried are superseded by more successful ones as our knowledge increases. The remarkable pace of technical developments suggests that it would be unwise to discount changes to human genes in the medium term. The rest of this chapter considers some of the possibilities and problems to look out for. Page 11 of 31 2nd March 2016 http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-therapy/contentsection-0 Gene therapy 3 Somatic gene therapy There is a distinction between somatic cells, those making up almost all of the body, and germline cells, which are the eggs and sperm and the cells that produce them. Somatic gene therapy is the transfer of genes into the somatic cells of the patient, such as cells of the bone marrow, and hence the new DNA does not enter the eggs or sperm. The genes transferred are usually normal alleles that could ‘correct’ the mutant or disease alleles of the recipient (see Study Note 2: The technique of somatic gene therapy). Study Note 2: The technique of somatic gene therapy The technique of somatic gene therapy involves inserting a normal gene into the appropriate cells of an individual affected with a genetic disease, thereby permanently correcting the disorder. Figure 2 outlines the simplest methods of getting genes into the person's cells using either viruses (which carry the human gene, in place of one of their own genes, into a cell) or liposomes (small fat-like molecules which can carry DNA into a cell). In some cells, the gene or genes become inserted into a chromosome in the nucleus. The target cells might be bone marrow cells, which are easily isolated and reimplanted. Bone marrow cells continue to divide for a person's whole life to produce blood cells, so this approach is useful only if the gene you want to deliver has a biological role in the blood. Delivery of a gene that has a biological role in, say, the lungs, muscle, or liver would have to occur within those target organs. In many cases, accessing the appropriate tissue or, if the gene is required in multiple tissues (e.g. muscles throughout the body) ensuring it can be delivered where it is needed, is a major problem. Page 12 of 31 2nd March 2016 http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-therapy/contentsection-0 Gene therapy Figure 2 The technique of somatic gene therapy View description - Figure 2 The technique of somatic gene therapy SAQ 4 Will somatic gene therapy prevent the treated person from passing on the defective gene to their children? View answer - SAQ 4 However, there are three major scientific hurdles that have to be overcome before somatic gene therapy is likely to work. The first is getting the human gene into the patient's cells (using viruses or liposomes, Study Note 2). Adverse results in a UK/French gene therapy trial in 2002, including the death of one patient, highlighted some of the risks of using viruses. Following a safety review, the trial resumed because of the severity of the disease, and by the end of 2004, 17 out of 18 patients treated had experienced some improvements in their condition, with four experiencing significant improvements. Unfortunately, in early 2005 the trial had to stop again when a patient suffered an adverse reaction. Clearly, there is still some way to go with respect to safety of the techniques. The second obstacle is getting the gene into the right cells. For example, for sickle cell disease (caused by defective haemoglobin in red blood cells), the cells to choose would be the patient's bone marrow cells. For cystic fibrosis, application in the lungs Page 13 of 31 2nd March 2016 http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-therapy/contentsection-0 Gene therapy and gut would be needed. The lungs might be accessible via an aerosol spray. Treating the gut would need some way to deliver genes in a package that the patient would swallow, and which would protect them from digestive enzymes until they could act. The final obstacle is making sure the gene is active, that is, switched on in the cell to produce the protein that the patient needs. This means it must be under the control of the sequence of DNA that is responsible for switching the gene on. The results do not have to be perfect to produce benefits. In cystic fibrosis, animal tests have shown that if the normal gene can be transferred to only five per cent of cells in the lungs, this restores some normal function. The prospects for somatic therapy for single-gene diseases are still improving. SAQ 5 Why is gene therapy an unrealistic option for multifactorial diseases? View answer - SAQ 5 In general, current efforts to treat disease by somatic gene therapy do not pose any novel ethical issues, provided there is proper enforcement of informed consent in trials. There is concern, however, about where the successful development of techniques for germline gene therapy might lead. Page 14 of 31 2nd March 2016 http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-therapy/contentsection-0 Gene therapy 4 Germline gene therapy Now that in vitro fertilization – bringing eggs and sperm together outside the prospective mother's body – is an established technology, the possibility exists that genes could be altered in eggs or sperm, or in a very early embryo. The obvious advantages of germline gene therapy are that the cells are accessible (because they are outside the body), so gene delivery is less of a problem than it tends to be with somatic cells; and the inserted gene (or genes) would be present in all the cells of the person so treated because it would be transmitted to progeny cells during growth and development. SAQ 6 Would a person who had received germline gene therapy transmit the inserted gene(s) on to their children? View answer - SAQ 6 This might be poor business for gene therapy companies, but could be good for people with a genetic disorder. Until recently, there was widespread agreement that germline gene therapy in humans should be ruled out. It is currently (early 2005) banned in the UK. It is not possible to predict where in the genome a newly inserted gene might end up, and this poses unknown risks of causing new mutations, or otherwise disrupting normal gene functioning. Even if these hazards could be removed, there are new ethical problems that could appear with serious development of germline therapy. These include how to decide which genetic alterations to permit. Some would clearly be aimed at correcting harmful mutations, but others might be considered enhancements, rather than treatments. Sometimes, it may be hard to tell the difference. Page 15 of 31 2nd March 2016 http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-therapy/contentsection-0 Gene therapy 5 Designer babies? A character under genetic influence where the distinction between treatment and enhancement is hard to draw is height. Treatment of short stature – with human growth hormone made in genetically manipulated bacteria – has already given rise to controversy about how short a child needs to be for treatment to count as meeting a medical need. That is, how tall is tall enough? As we identify genes that have effects on many other human characters, from appearance to, perhaps, intelligence, developing techniques for germline gene therapy could in principle open the way to wider attempts to influence the phenotype of the next generation. Even if experiments in humans are ethically barred, commercial and medical interests are driving the technology forward in animals (remember those genetically modified sheep). So far, the vast majority of those working with the technology have rejected the idea of germline gene therapy because of fears about ‘designer babies’, as well as wariness of more immediate hazards such as the ones previously outlined (Section 4). In the last few years, though, arguments in favour of permitting some use of germline therapy have been heard more often. SAQ 7 What do you think the argument in favour might be? View answer - SAQ 7 Although ‘bad’ genes might be eliminated, might ‘good’ genes be added, such as those that contribute to intelligence, appearance or personality? Might the technique lead to the birth of eugenics – the science of improving the human condition through selective breeding – a belief held in the early decades of the 20th century? You might like to think about whether you would vote to permit doctors to alter germline cells by inserting a new gene or genes. And would you change your views if the gene or genes in question gave the resulting baby immunity to HIV, the virus that causes AIDS (acquired immunodeficiency syndrome)? In the longer term, the advent of reliable techniques for altering human genes could lead to genuinely new ethical problems that are difficult to outline in conventional terms. Most generally, moral philosophers have nearly always argued about justice in terms of inequalities arising from social differences between individuals – such as wealth, class, education and so on. But if we have the ability to alter or ‘correct’ inherited characters, we might have to try to work out a theory of justice that covered what we have always regarded as natural differences between individuals. Some of these issues have already been raised by recent developments in in vitro fertilization and reproductive technologies, and thus may indicate the kinds of debates that could take place around germline gene therapy. For example, embryos can be Page 16 of 31 2nd March 2016 http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-therapy/contentsection-0 Gene therapy tested for genetic conditions, with only those free of affected alleles being implanted into the uterus. This technique can be used to test for diseases such as cystic fibrosis, which have traditionally been seen as obvious candidates for gene therapy. The end result (the removal of that genetic condition from that family) is the same as that produced by gene therapy. If gene therapy is eugenic, then surely the same can be said of such embryo testing which has the added advantage of avoiding the unpredictability of gene insertion (see Section 4). Yet there seems very little public concern about these current reproductive technologies, which may suggest that germline gene therapy may well be acceptable if, or when, it becomes available. Activity 1: Application of genetic technologies Click to read the article on 'Selection of the fit and cancer-free'. Imagine that a friend has just read 'Selection of the fit and cancer-free', and she is puzzled about the meaning of the term ‘designer babies’ because the technology described in some detail in the article is different from the technology described in the section above on this subject. She asks you to write to her explaining, in about 280– 300 words, how these two technologies could be used to produce designer babies in the future. You should answer using your own words. She is familiar with most biological terms (including gene, screening, gene therapy, embryo), so you don’t have to define them. After having considered her question you may decide that you have to explain the meaning of the term ‘designer babies’ and the similarities and the differences in the two technologies outlined in sections 4 and 5 above. Bear in mind that you should aim for your explanation to be as concise, cohenrent and clear as possible. When you have completed your explanation compare it with the version that we have written in the comments below. View answer - Activity 1: Application of genetic technologies Page 17 of 31 2nd March 2016 http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-therapy/contentsection-0 Gene therapy Conclusion This free course provided an introduction to studying Science. It took you through a series of exercises designed to develop your approach to study and learning at a distance and helped to improve your confidence as an independent learner. Page 18 of 31 2nd March 2016 http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-therapy/contentsection-0 Gene therapy Keep on learning Study another free course There are more than 800 courses on OpenLearn for you to choose from on a range of subjects. Find out more about all our free courses. Take your studies further Find out more about studying with The Open University by visiting our online prospectus. If you are new to university study, you may be interested in our Access Courses or Certificates. What’s new from OpenLearn? Sign up to our newsletter or view a sample. For reference, full URLs to pages listed above: OpenLearn – www.open.edu/openlearn/free-courses Visiting our online prospectus – www.open.ac.uk/courses Access Courses – www.open.ac.uk/courses/do-it/access Certificates – www.open.ac.uk/courses/certificates-he Newsletter – www.open.edu/openlearn/about-openlearn/subscribe-the-openlearnnewsletter Page 19 of 31 2nd March 2016 http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-therapy/contentsection-0 Gene therapy Page 20 of 31 2nd March 2016 http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-therapy/contentsection-0 Gene therapy Acknowledgements The content acknowledged below is Proprietary (see terms and conditions) and is used under licence. This content is made available under a Creative Commons AttributionNonCommercial-ShareAlike 4.0 Licence Grateful acknowledgement is made to the following sources for permission to reproduce material in this course: Course image: University of Michigan School of Natural Resources & Environment in Flickr made available under Creative Commons Attribution 2.0 Licence. Article: Selection of the fit and cancer-free; women undergoing IVF treatment could soon be able to select embryos. By Emma Brady, Birmingham Post, 29 April 2005. Don't miss out: If reading this text has inspired you to learn more, you may be interested in joining the millions of people who discover our free learning resources and qualifications by visiting The Open University - www.open.edu/openlearn/free-courses Page 21 of 31 2nd March 2016 http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-therapy/contentsection-0 Gene therapy SAQ 1 Answer It could mean treatment that involves correcting genes that are involved in causing an illness in an individual. Or, it could mean using genes to treat an illness caused in some other way. Back Page 22 of 31 2nd March 2016 http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-therapy/contentsection-0 Gene therapy SAQ 2 Answer All that happens is that the protein is extracted and given to patients, usually by injection on a regular basis, so the gene is not being corrected or repaired. Back Page 23 of 31 2nd March 2016 http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-therapy/contentsection-0 Gene therapy SAQ 3 Answer The gene would need to be active – get transcribed into mRNA and translated into protein. And it would have to enter the right cells. Back Page 24 of 31 2nd March 2016 http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-therapy/contentsection-0 Gene therapy SAQ 4 Answer No, because the gene they receive in somatic gene therapy does not enter their gametes. Back Page 25 of 31 2nd March 2016 http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-therapy/contentsection-0 Gene therapy SAQ 5 Answer Because a number of genes are involved, multiple gene therapy would be required. Back Page 26 of 31 2nd March 2016 http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-therapy/contentsection-0 Gene therapy SAQ 6 Answer They would also pass it on, because it would be present in their germline cells as well as their somatic cells. Back Page 27 of 31 2nd March 2016 http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-therapy/contentsection-0 Gene therapy SAQ 7 Answer Disease alleles would be eliminated. Back Page 28 of 31 2nd March 2016 http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-therapy/contentsection-0 Gene therapy Activity 1: Application of genetic technologies Answer Below is only one possible explanation. In comparing your answer with ours, ensure that you clearly explain the meaning of the term ‘designer babies’ and that you have noted the similarities and the differences in the two technologies (described in sections 4 and 5 and in the article on selection). Designer babies is a term used to describe babies that have enhanced, or designed, characters as a result of some kind of manipulation. The characters might be increased height, intelligence or appearance. Both the article and the course book link the use of the term ‘designer babies’ to that of in vitro fertilization (IVF), which allows scientists to bring sperm and eggs together to produce an embryo outside of the prospective mother’s body, making them accessible to manipulation by one of two types of technology. The first technology is screening of IVF embryos (i.e. pre-implantation genetic diagnosis) for the presence of particular characters. One cell can be removed from an early embryo and analysed to see if it carries harmful genes either for a genetic syndrome or associated with cancer. Such embryos would not be chosen for implantation into the potential mother’s uterus. However, embryos could also be checked for the presence of genes that confer cosmetic or enhanced features, and chosen for implantation to produce designer babies. The other technology which might be used to produce designer babies, is germline gene therapy. Using this technique, the gene(s) can be inserted in the sperm, egg or early embryo whilst the cells are outside the body. The gene(s) are carried by viruses or liposomes into cells. Once here, the gene(s) can become inserted into a chromosome and transmitted to the progeny cells. The inserted gene(s) might correct mutated genes, which is why the technology is being developed, but it might also be chosen to enhance the characters of the future individual. There are 260 words in the above answer. Explaining terms or phrases like this is a useful exercise because it forces you to think more probingly about the science, and tests that you have understood it. Back Page 29 of 31 2nd March 2016 http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-therapy/contentsection-0 Gene therapy Figure 1 The technique of genetic manipulation or genetic modification of organisms Description Figure 1 Back Page 30 of 31 2nd March 2016 http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-therapy/contentsection-0 Gene therapy Figure 2 The technique of somatic gene therapy Description Figure 2 Back Page 31 of 31 2nd March 2016 http://www.open.edu/openlearn/science-maths-technology/science/biology/gene-therapy/contentsection-0